Fix deploy-preview: handle missing prod DB gracefully

Production still uses JSON, so /data/planner.db doesn't exist yet.
Detect cp failure and use empty DB (init_db creates tables on startup).

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

scripts/deploy-preview.py

@@ -78,14 +78,20 @@ def deploy(pr_id: str):
     ).stdout.strip()
 
     if prod_pod:
-        kubectl("cp", f"{PROD_NS}/{prod_pod}:/data/planner.db", "data/planner.db")
+        r = kubectl("cp", f"{PROD_NS}/{prod_pod}:/data/planner.db", "data/planner.db", check=False)
+        if r.returncode != 0 or not Path("data/planner.db").exists() or Path("data/planner.db").stat().st_size == 0:
+            print("  WARNING: Could not copy prod DB, using empty DB")
+            Path("data/planner.db").touch()
     else:
         print("  WARNING: No running prod pod, using empty DB")
         Path("data/planner.db").touch()
 
     # 2. Build and push image
     print("[2/5] Building Docker image...")
-    dockerfile = textwrap.dedent("""\
+    # Only COPY DB if it has content, otherwise let init_db create fresh
+    has_db = Path("data/planner.db").exists() and Path("data/planner.db").stat().st_size > 0
+    copy_db_line = "COPY data/planner.db /data/planner.db" if has_db else "RUN mkdir -p /data"
+    dockerfile = textwrap.dedent(f"""\
         FROM node:20-slim AS frontend-build
         WORKDIR /build
         COPY frontend/package.json frontend/package-lock.json ./
@@ -99,7 +105,7 @@ def deploy(pr_id: str):
         RUN pip install --no-cache-dir -r requirements.txt
         COPY backend/ ./backend/
         COPY --from=frontend-build /build/dist ./frontend/
-        COPY data/planner.db /data/planner.db
+        {copy_db_line}
         ENV DB_PATH=/data/planner.db
         ENV FRONTEND_DIR=/app/frontend
         ENV DATA_DIR=/data